This invention generally relates to a method for forming a thermoplastic container. More particularly, this invention relates to such a method in which the container finish is injection molded in a neckring and a tubular parison then formed by relative movement of the finish portion and the material orifice. Specifically, this invention relates to such a method in which the tubular parison is removed to a final blow station for formation into a finished container to allow formation of a new tubular parison during the blowing of the previously formed tubular parison.
The present invention is concerned with an improved operational method for a plastic bottle forming machine of the type generally shown in U.S. Pat. No. 3,019,480 and 3,008,192, the teachings of which are hereby incorporated by reference. This general type of plastic bottle forming machine utilizes a neck mold or neckring into which a charge of plastic material is injected to thereby form the finish portion of the plastic bottle. The mold is then moved upwardly as plastic material is allowed to continue to extrude from the orifice thereby pulling an elongated tubular parison. When the desired length of parison is reached, a final blow mold closes about the parison and the bottle is blown to final shape by high pressure air. The finished container is then removed from the orifice area and the neck mold moved downwardly into intimate contact with the orifice for injection of a new finish portion and repetition of the cycle. It is clear from this description of the forming cycle that this type of machine could be described as a series type machine. That is, all the operations for the formation of a single plastic container take place in the same general location. It is therefore not possible to form a parison in one location and transfer it to a second location for blowing while a new parison is simultaneously being formed. While machines of the type described have met with substantial commercial success and are in general use throughout the world, this limitation in speed has to some extent limited their overall acceptance and usefulness. Of course, such machines commonly utilize multiple orifices and blow molds so that a number of bottles, six to eight for example, are being formed simultaneously. However, it would be desirable to change the cycle of such a machine to a parallel type operation in which the formed parison may be removed to a separate location for final blowing while a new parison is simultaneously being injected and drawn. It is to this end that the operational method of the present invention is directed. U.S. Pat. No. 3,048,890 is one example of an attempt to improve the process cycle of plastic forming machines of this general class. However, this particular patent required the installation of two separate extrusion orifices and two separate turntables to carry blow molds and neckrings. Additionally, this particular patent taught a rather complex and involved overlapping forming cycle, which would require basic redesign of the plastic forming machine. The present invention would allow utilization of the basic forming machines as they now exist with some modification to meet the demands of this new cycle.